The present invention relates in general to data processing systems, and in particular, to the rendering of graphics objects using fixed-point arithmetic.
Graphics application programming interfaces (APIs) commonly implemented in data processing systems, particularly personal computers (PCS), and workstations allow an application to define lighting parameters as floating-point numbers. Consequently, the graphics hardware, or engine, generates the lighting values in response to an underlying lighting model using floating-point operations. These lighting values are then loaded into a frame buffer, which drives a display device, as fixed-point numbers having a predetermined number, n, of bits. For example, the data values in the frame buffer may be eight-bit values corresponding to 256 color levels.
In the graphics hardware, it is faster and less expensive from a resource standpoint to perform fixed-point operations rather than floating-point operations. Thus, there is a need in the art for an apparatus and method for performing graphics lighting using fixed-point operations, without suffering a loss of accuracy relative to graphics lighting performed using floating-point calculations.
The aforementioned needs are addressed by the present invention. Accordingly there is provided, in a first form, a fixed-point graphics apparatus. The apparatus contains first logic that is operable for converting a first operand to a first fixed point data value having a preselected number of bits. The first logic generates the first fixed point data value using a first predetermined scaling in response to the preselected number of bits. The apparatus further includes second logic that is operable for converting a second operand to a second fixed point data value having the preselected number of bits. The second logic generates the second fixed point data value using a second predetermined scaling in response to the preselected number of bits and a number of bits in a color data value. The first and second fixed point data values are operable for generating a color data value in accordance with a preselected lighting model.
There is also provided, in a second form, a fixed-point graphics method. The method includes converting a first operand to a first fixed point data value having a preselected number of bits. The method converts using a first predetermined scaling in response to the preselected number of bits. A second operand is converted to a second fixed point data value having the preselected number of bits using a second predetermined scaling in response to the preselected number of bits and a number of bits in a color data value. The first and second fixed point data values are operable for generating a color data value in accordance with a preselected lighting model.
Additionally, there is provided, in a third form, a data processing system. The data processing system contains a memory, a central processing unit (CPU), and a fixed-point graphics unit. The fixed-point graphics unit is operable for receiving one or more first and second floating point operands from the CPU in response to at least one of the instructions stored in the memory which corresponds to a preselected graphics application programming interface (API). The fixed point graphics unit includes logic operable for converting the first operands to corresponding fixed point data values having a preselected number of bits. The logic generates the fixed point data value using a predetermined scaling in response to the preselected number of bits. The fixed-point unit also includes logic operable for converting the second operands to corresponding second fixed point data values having the preselected number of bits. The second fixed point data values are generated by the logic using a second predetermined scaling in response to the preselected number of bits and a number of bits in a color data value. The first and second fixed point data values are operable for generating a color data value in accordance with a preselected lighting model corresponding to the API.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.